Hydrogen peroxide, H.sub.2 O.sub.2, is a commodity chemical used in many industrial processes. Hydrogen peroxide has been commercially available since the middle of the 19th Century in the form of aqueous solutions of hydrogen peroxide within broad concentration ranges, typically between 1 and 80 weight percent, and can be as concentrated as 96 weight percent. The major chemical properties and uses of hydrogen peroxide result from its structure which includes a covalent oxygen-oxygen (peroxy oxygen) high energy-bond. The high energy peroxy bond provides the chemical driving force that makes hydrogen peroxide useful in many chemical processes. More particularly, hydrogen peroxide is used in a variety of organic and inorganic oxidation reactions, and can be used to make a variety of other organic and inorganic peroxy compounds. An important use for hydrogen peroxide is in the dissolution of metal, typically copper, from a masked printed wiring board substrate to form a final wiring pattern. Typically the aqueous hydrogen peroxide etchant compositions comprise in an aqueous solution, an active amount of hydrogen peroxide, a strong mineral acid and an organic stabilizer.
While the high energy perioxy bond of hydrogen peroxide provides a chemical driving force useful to chemists, the high energy bond can also result in (1) the tendency of hydrogen peroxide to decompose into water, H.sub.2 O and oxygen gas, O.sub.2, and (2) the tendency to oxidize organic compounds in the peroxide solutions. Highly pure hydrogen peroxide in a suitable inert container is relatively stable. However, commonly available industrial grades of hydrogen peroxide are typically contaminated during manufacture, transfer, storage and use by chemical impurities that can catalyze or at least support decomposition. The most common decomposition catalysts comprise di- or tri-valent metal ions. Stabilizers have been developed and are now commonly used to reduce decomposition to the lowest achievable level by minimizing the effect of the impurities. Examples of known stabilizing agents are 8-hydroxyquinoline, sodium pyrophosphate, stannic acid, sulfolene, sulfolane, sulfoxide, sulfone, dialkylaminothioxomethyl, thioalkylsulfonic acids, aliphatic amines, benzotriazole, nitro-substituted organic compounds such as nitrobenzene sulfonic acids, thiosulfate, and others. Such stabilizers are known in a number of prior art publications.
Solenberger, U.S. Pat. No. 3,801,512, discloses an inorganic acid, hydrogen peroxide etchant containing a stabilizer such as alkyl-anilines. Solenberger further states in column 3, lines 23-25 that examples of alkyl-anilines which may be utilized in the present invention include C.sub.1-4 alkyl derivatives.
Shibasaki et al., U.S. Pat. No. 3,773,577, discloses a sulfuric acid hydrogen peroxide etchant solution containing an additive such as N,N-dialkylaniline.
As an etchant for the manufacture of printed wiring boards, aqueous hydrogen peroxide solutions are attractive because hydrogen peroxide solutions are relatively easily handled, have high activity and low cost. However, hydrogen peroxide metal etching compositions can be subject to numerous problems and pitfalls. Since large amounts of metallic ions are generated during etching, the metallic ions can promote rapid hydrogen peroxide decomposition, thus destroying substantial proportions of the hydrogen peroxide that should economically be used directly in the removal of metal from printed wiring board circuits. Etchants that can be stabilized, during storage and use, from substantial decomposition of hydrogen peroxide are desirable for convenient and effective etchant processes. Further, the etchant compositions should be stabilized from loss of the organic stabilizers. Still further, the rate of etching using hydrogen peroxide etchants can be accelerated using organic promoters.